1. Field of the Invention
The present invention relates to a drive controlling apparatus, and more particularly, it relates to a drive controlling apparatus used in a sheet supplying apparatus provided in an image forming apparatus.
2. Related Background Art
Conventional image forming apparatuses such as copying machines, printers and the like each has a sheet supplying apparatus in which a drive controlling apparatus for controlling the driving of a sheet supply roller is used.
An example of a conventional drive controlling apparatus for a sheet supply roller is shown in FIG. 18. Such a drive controlling apparatus includes a sheet cassette portion, a drive portion, a sheet supply roller portion and a lock portion. Now, these portions will be briefly described.
First of all, the sheet cassette portion comprises a sheet cassette 108 and sheets 100, and the sheet cassette is provided with an intermediate plate 108 pivotable around a fulcrum 108a, and projections 108c are provided on a downstream (in a sheet supplying direction) end portion of the intermediate plate. Springs 108d disposed below the intermediate plate serve to bias the intermediate plate 108b in a direction shown by the arrow X.
Forces exerted by the springs 108d act on cams 121a of the sheet supply roller portion 121 through the projections 108c to tend to rotate the cams in a direction shown by the arrow Y. Thus, a sheet supply roller 109, a notched gear 121b and a locking member 121c which are secured to a rotary shaft 120 together with the cams 121a also tend to rotate in the direction Y. However, since a locking pawl 121d formed on the locking member 121c is engaged (locked) by a stopper 122, the sheet supply roller the sheet supply roller portion is entirely held stationary.
When the locking pawl 121d is disengaged from the stopper 122, the entire sheet supply portion 121 is rotated in the direction Y by a predetermined angle, with the result that a toothed portion of the notched gear 121d is engaged by a drive gear 127 rotated by a motor M in a direction W. Consequently, the sheet supply portion 121 is rotated by one revolution until a condition shown in FIG. 18 is restored again. After one revolution, when a non-toothed portion 121e of the notched gear 121b is opposed to the drive gear 127 again, the locking pawl 121d is locked by the stopper 122 again.
The engagement and disengagement between the locking member 121c (locking pawl 121d) and the stopper 122 is effected by a spring 122c for biasing the stopper 122 in a direction Z and a lock releasing portion for urging the stopper 122 in opposition to the force of the spring 122c.
That is to say, when the disengagement is effected, a locking member 123c of the lock releasing portion is rotated to urge the stopper 122 in opposition to the force of the spring thereby to disengage the stopper 122 from the locking pawl 121d of the sheet supply roller portion, thus starting the rotation of the sheet supply roller portion. Other than the above disengagement, the stopper 122 is always urged against the locking member 121c of the sheet supply roller portion by means of the spring 122c.
Now, the lock releasing portion will be described.
The lock releasing portion includes a cam 123a, a notched gear 123b, a locking member 123c (which are mounted on a common rotary shaft), a leaf spring 125 for applying a rotational force to the cam 123a, and a solenoid 126 for controlling the timing of rotation. In the condition shown in FIG. 18, although the cam 123a tries to rotate in a direction V by the action of the leaf spring 125, since a locking pawl 123d of the locking member 123c is locked by a solenoid actuator 126a, the entire lock releasing portion is held stationary.
When current is applied to the solenoid 126 to retract the solenoid actuator 126a toward the solenoid 126, the locking pawl 123d of the locking member 123c is disengaged from the solenoid actuator 126a, with the result that the cam 123a is rotated by the action of the leaf spring 125 by a predetermined angle. During this rotation, since a toothed portion of the notched gear 123b is engaged by the drive gear 127, the cam 123a continues to rotate by one revolution. After one revolution of the cam 123a, when a non-toothed portion of the notched gear 123b is opposed to the drive gear 127 again (FIG. 18), the locking pawl 123d of the locking member 123c is locked by the solenoid actuator 126a again, thereby stopping the cam.
In such a drive controlling apparatus using the notched gear, a force for rotating the notched gear until the toothed portion is engaged by the drive gear (this force is referred to as "rotation starting force" hereinafter) is required.
However, in the above-mentioned conventional drive controlling apparatus, as mentioned above, since the rotation starting force is obtained by the springs 108d disposed below the intermediate plate 108b and is transmitted directly to the notched gear 121b through the cams 121a of the sheet supply roller portion 121, the rotation starting force becomes excessive. The reason is that the springs 108d must provide a strong biasing force sufficient to urge the sheets 100 stacked in the cassette against the sheet supply roller 109 and this strong biasing force acts on the cams 121a as the rotation starting force.
However, due to such strong rotation starting force, the following problems arise. Firstly, since the strong rotation starting force increases the locking force between the locking pawl 121d of the sheet supply portion 121 and the stopper 122, it is impossible to release such a locking force by using a solenoid, and, thus, the above-mentioned lock releasing portion must be provided. As a result, the entire apparatus becomes complicated.
Secondary, due to the strong rotation starting force, after the lock is released, when the notched gear 121b is engaged by the drive gear 127, the excessive force acts on the drive gear, with the result that the rotational speed of the drive gear is increased by an amount corresponding to backlash between a gear of the motor M and the drive gear (refer to FIG. 19).
Other than the above-mentioned arrangement in which the rotation starting force is obtained by the springs disposed below the intermediate plate, even when an arrangement in which a rotation starting force is obtained from an independent spring is used as disclosed in Japanese Patent Application Laid-open No. 2-193830, a biasing force of such a spring acts as a rotational force for rotating a sheet supply roller via a cam, and, when a notched gear is engaged by a drive gear after the lock is released, the excessive force also acts on the drive gear.
The increase in the rotational speed of the drive gear affects an influence upon all of gears associated with the drive gear. For example, as is in a normal case, when the drive gear is associated with a convey roller gear for directly conveying a sheet to a transfer portion, a rotational speed of the convey roller is also increased to push the sheet into the transfer portion excessively, thereby causing deviation of an image and worsening image quality. Further, the convey speed of the entire convey portion is unbalanced, thereby causing sheet jam.
The above problems may be caused in general drive controlling apparatuses. Thus, there is a need for providing a drive controlling apparatus for transmitting rotation from a drive source to a rotary shaft, in which the initiation of rotation of the rotary shaft does not affect an influence upon the drive source.